I had the same issue to when posting a polygon where first three coordinates would be co-linear. The polygon as such should be valid, because for example the forth point may not be co-linear.
In AbstractSDOEncoder , method addPolygon it checks whether the exterior ring of the polygon isCounterClockwise , which is a function in NumericalMethods . Here it only checks for the first three coordinates. I wonder whether it would be ok to iterate through the points to perform this check.
Meanwhile I'll try to find another workaround. I tried removing the collinear vertices with JTS, but it didn't help :
JTS.removeCollinearVertices(geom);
Thanks for your hard work.